From practice, essentially two variants of rack change systems for switching of roller racks of a rolling block are known. Such rack change systems are based on change carriages for receiving the roller racks. Typically, at least two independently movable carriages are used. However, embodiments are also known in which only one carriage or two rigidly connected carriages are used.
The first variant of a rack change system (I type) known from practice is characterized in that a rail track for the change carriage is arranged parallel to the rolling line in front of the rolling block. The one change carriage serves for receiving prepared new roller racks and the second change carriage serves for receiving roller racks present in the rolling block. During the roller rack change process, the rolling block drives are stopped and a protective hood is opened and the couplings in the rolling block are separated so that the roller racks can be pushed onto the waiting, empty rack change carriage, using a suitable device on the rolling block. Subsequently, both change carriages move in the direction of the rolling line so that the change carriage with the new roller racks stops in front of the rolling block and the roller racks can be pushed into the rolling block again, using a suitable device. After coupling the roller rack and closing the protective hood, the rolling operation can be resumed. Embodiments are known from practice in which this process typically takes between 3 and 5 minutes.
After the change process has been completed and the rolling operation has been resumed, the change carriage can be unloaded by a crane and the changed roller racks can be transported to the rack workshop. Likewise, the empty change carriage can again be loaded with newly prepared roller racks by a crane, the roller racks having been transported from the roller workshop.
The advantage of this variant lies in the short travel time of the change carriage in front of the rolling block and the associated short rack change time. The disadvantage is the involved and time-consuming loading and unloading of the change carriage by means of a hall crane in the mill as well as the non-automated transport of the roller racks to and from the rolling block in the roller workshop.
In this variant, the change carriages can only be moved independently of each other if they are each equipped with their own drive. This can be, for example, an electrically operated drive for the wheels. To this end, the change carriage has to be coupled with a power supply, which is generally implemented by means of a drag chain. Thus, the possible travel path of the change carriage is significantly limited. A more favorable cable system, the drive of which is arranged stationary in the hall floor, can be present only once on a travel path, however, so that, in one embodiment of the variant with the cable system described above, both change carriages must be firmly coupled to each other or, alternatively, a suitably large change carriages must be used that can accommodate both, the used as well as the new, prepared roller racks.
In the second variant known from practice, a track of a rail system is provided that extends transversely to the rolling line and in the direction of the roller block. Set at a certain distance from the rolling block, a rotary switch is provided. Via the rotary switch, another track is connected to the track arranged transverse to the rolling line. This additional track, arranged at a right angle to the main direction of travel, allows for a parking or waiting position for a change carriage. This second variant (T type) requires that at least two independently movable change carriages are available.
During the rack change in the second variant, an empty change carriage is provided at the end of the track transverse to the rolling line. After stopping the rolling block drives, opening the protective hood, and uncoupling the racks, the racks are pushed onto the empty change carriage, waiting in front of the block. Once this process is completed, the change carriage travels to the position of the rotary switch and stops there. Then the four wheels of the change carriage are rotated 90° by means of the rotary switch and the carriage can be moved to the park position by means of a second cable system. Once the change carriage has arrived there, the rotary switch can again be rotated 90° and the second carriage waiting behind the switch with the new racks can be coupled into the first cable system and driven in front of the rolling block. Once the second change carriage has arrived there, the prepared roller racks are pushed into the roller block, the racks are coupled in, the hood is closed, and the rolling operation can continue. Subsequently, the rotary switch is rotated again by 90° so that the change carriage parked by means of the second cable system can leave the park position again and moves onto the rotary switch. Once it has returned to this position, after another actuation of the rotary switch, it can be driven into the roller workshop over the track transverse to the rolling line where it can be unloaded and be loaded again with new prepared roller racks. Subsequently, the prepared change carriage moves back to the waiting position behind the rotary switch (viewed from the rolling block).
The advantage of the second variant (T type) over the first variant (I type) of the rack change system is the possibility of driving the change carriage directly into the roller workshop. This avoids the cumbersome reloading of the racks onto another transportation system. However, a disadvantage of this variant is the significantly longer rack change time, which, due to the additional multiple switching of the switch and the additional transverse drive of the change carriage, results in a rack change time lasting 2 to 3 minutes longer, and therefore a longer break in production of the entire mill.
The rack change system of the second variant (T type) allows for the use of a stationary drive system of the change carriage (for example, a cable system). Thereby, a separate system must be provided for each driving direction. This makes it possible to implement travel paths of any length since the rack change carriage does not require its own on-board drive system, and therefore no separate power supply.
For the efficient operation of pipe, profile, rod, and wire mills, minimizing the rack change times is of significant importance. Due to increasingly smaller batch sizes and frequent dimensional changes in production, replacement of the roller racks is required in ever shorter intervals. Each rack change results in a break in production, which reduces the total output of the mill. For this reason, the rack change times are of crucial importance for the productivity of the rolling mill.